A Jimmy John's delivery man wears shorts as he rides a bike on Tuesday, Feb. 18, 2013, in Minneapolis, as temperatures rose into the 40s. / David Joles, AP

by Doyle Rice, USA TODAY

by Doyle Rice, USA TODAY

The warm-up this week across much of the nation will bring a welcome break from the harsh winter cold. However, the mild air and some heavy rain - coupled with the thick blanket of snow - will also bring the potential for river floods, ice jams, roof collapses and black ice at night.

High temperatures are forecast to be in the 40s this week from the Upper Midwest to New England. On Tuesday, Chicago hit 46 degrees, the first time in five weeks the city had reached 40 degrees or higher, according to the National Weather Service.

Due to the warming temperatures and predicted rainfall, the states that could see some minor to possibly moderate flooding later this week are Ohio, Indiana, Illinois and Michigan, according to Mary Mullusky, a hydrologist with the National Weather Service.

In particular, she predicted that the Wabash River (in Ohio and Indiana) and the White River (in Indiana) could see flooding.

"Rapid snow melt and locally heavy rainfall is possible on Thursday," notes an online forecast from the weather service in Indianapolis, discussing the possible floods in central and southern Indiana. "This may cause flooding in low-lying areas, basements, small streams and creeks."

"Should a significant rain event occur on Thursday, the severity of the flooding would greatly increase," the forecast warned.

From 1 to 2 inches of rain is forecast to drench portions of the Mississippi and Ohio valleys on Thursday and Friday, according to AccuWeather.

Ice jams are also possible in parts of the Northeast this week, Mullusky said. This occurs when thawing rivers release huge chunks of ice, blocking the flow of the river and leading to flooding.

Snow can also lead to roof collapses: "A deep snow varied by drifting, combined with rainfall, natural melting and blocked drainage systems on the roofs can lead to uneven weight distribution," according to AccuWeather forensic weather expert Steve Wistar. "When this weight exceeds the design of the roof, a partial or total collapse could occur," he said.

Another issue is when the melting snow turns to black ice at night and in the early morning, which can be a danger to motorists and pedestrians, said AccuWeather meteorologist Alex Sosnowski. He said that with communities running out of salt and sand, there may be more black ice on the roads.

The warm-up this week will be short-lived, as a return to bitter cold and possible snow is likely next week. The final week of February may trend quite cold yet again in much of the eastern two-thirds of the nation, according to The Weather Channel.

The National Oceanic and Atmospheric Administration will issue its spring flood outlook on March 20, which, appropriately enough, is the first day of spring. The main spring flood season usually occurs in April.

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